U.S. EPA Continues Drive Towards First EV Charger Efficiency Specs

Wed, 11/30/2016 - 11:06 -- MrGreen

The U.S. Environmental Protection Agency (EPA) is getting close to its year end goal of delivering a final draft EV charger efficiency program specification. When published, the ENERGY STAR® program will be the world's first efficiency program covering Level 1 and Level 2 Electric Vehicle Service Equipment (EVSE)1.

As discussed in an earlier Mr. Green blog, the program's aim is to limit the amount of power consumed when an EVSE is in idle or partial-on mode and not actively charging the vehicle's battery2.

Last August's Version 1, Draft 2 program specifications contained the following changes from the original draft:

  • Modal State Definitions: The EPA has clarified the relationship between the operational modes used in the program specification (i.e. off, on, idle, partial-on) with the industry standard definitions in SAE J1772 (i.e. states A, B, C).
  • Expanded Test Dataset: Test data from additional models have been added to allow setting more realistic efficiency requirements.
  • Auto power down requirement removed: Since an EVSE can only power down after being disconnected from the EV, the EPA is removing this requirement. Stringent partial-on requirements will ensure the powering down of non-essential EVSE features, according to the EPA.

The formulas for calculating partial-on and idle mode power consumption limits remain unchanged in Draft 2, but some functional power allowances used in the calculations were relaxed, based on new test data. And in late October, the EPA issued a follow-up memo proposing an additional efficiency requirement for a "no-vehicle" mode. No-vehicle mode occurs when the EVSE is connected to mains power, but not connected to an EV. In this mode, power might still be provided for tertiary functions, such as an EMC filter and mode status indicators. No-vehicle mode is expected to be the lowest EVSE power mode.

Shown below are the requirements for no-vehicle, partial-on, and idle modes.

No-vehicle mode requirement
The measured no-vehicle mode power (PNO_VEHICLE) must be ≤ the maximum no-vehicle mode power requirement (PNO_VEHICLE_MAX) as calculated below:

Where: PNO_VEHICLE_MAX is the maximum no-vehicle mode power requirement, PNO_VEHICLE_BASE = base no-vehicle mode power allowance for all products (see table 1 below), PWAKE_i = no-vehicle mode power allowance for each active, in-use networking/control protocol giving remote hosts the ability to wake the EVSE from no-vehicle mode, for a total of n allowances.

Partial-on mode requirement
The measured partial-on mode power (PPARTIAL_ON) must be ≤ the maximum partial-on mode power requirement (PPARTIAL_ON_MAX) as calculated below:

Where: PPARTIAL_ON_MAX = maximum partial-on mode power requirement, PPARTIAL_ON_BASE = base partial-on mode power allowance for all products (see table 1 below), PWAKE_i = partial-on mode power allowance for each active, in-use networking/control protocol giving remote hosts the capability to wake the EVSE from partial-on mode, for a total of n allowances.

Idle mode requirements
The measured idle mode power (PIDLE) must be ≤ the maximum idle mode power requirement (PIDLE_MAX) as calculated below:

Where: PIDLE_MAX = maximum idle state power requirement (W), max current is the nameplate maximum current (A), and PIDLE_BASE = base idle mode power allowance for all products, (see table 1 below), PIDLE_i = idle state power allowance for each applicable product function listed below, for a total of n allowances.

The EPA is proposing using the same base and functional power allowances for the three modes, as shown in Table 1 below.

Table 1. Power Allowances for All Modes (except where noted)

Product FunctionPower Allowance (W)
Base Allowance for All Products (PPARTIAL_ON_BASE, PIDLE_BASE, PNO_VEHICLE_BASE)2.6
In-use Wi-Fi or Ethernet Interface with Wake Capability (PIDLE_i, PWAKE_i) 1.0
In-use Cellular with Wake Capability (PIDLE_i, PWAKE_i)2.0
Other In-use LAN (Local Area Network) Protocol with Wake Capability (PIDLE_i, PWAKE_i)1.0
In-use Display (PIDLE_i, PWAKE_i) (Applies to no-vehicle mode and idle mode only)PON_MAX = (4.0 × 10-5 × ℓ × A) + 119 × tanh (0.0008 × (A – 200.0) + 0.11) + 6.0

Where: A = screen area (in2), ℓ = maximum measured display luminance (candelas per m2), and tanh is the hyperbolic tangent function

For more information, including a copy of the Version 1, Draft 2 spec and the October 28th follow-up memo, visit the ENERGY STAR Electric Vehicle Supply Equipment webpage.

  1. Level 1: a galvanically-connected EVSE with a single-phase input voltage nominally 120 volts AC and maximum output current ≤16 amps AC. Level 2: a galvanically-connected EVSE with a single-phase input voltage from 208 to 240 VAC and maximum output current < 80 amps AC.
  2. Idle mode is when an EVSE is connected to mains power and can promptly provide its primary function, but isn't doing so. Partial-on mode is when an EVSE provides at least one secondary function but no primary one. Secondary functions include full network connectivity, occupancy sensing, vehicle communications, and illumination of the display and its automatic brightness control.